1) Field of the Invention
The present invention relates to a curing agent for epoxy resins comprising a polyamine compound having a specific structure as a curing agent for epoxy resins, a polyether-modified polysiloxane and an amino group-modified polysiloxane, an epoxy resin composition comprising said curing agent composition for epoxy resins and an epoxy resin cured product obtained by curing said epoxy resin composition.
2) Related Art
It has been well known that various polyamine compounds are widely used as a curing agent for epoxy resins and a raw material thereof. The epoxy resin compositions using these curing agents for epoxy resins are particularly utilized widely in a field of coating materials such as a corrosion-resistant paint for ships, bridges and land and marine iron structures and a field of civil engineering and construction such as materials for lining, reinforcement or repair of concrete structures, flooring materials of buildings, linings of water supply and sewerage systems, pavement materials, and adhesive materials.
Among these polyamine compounds, a diamine represented by the following formula (I) and a curing agent for epoxy resins using said diamine as a raw material have features such that they can provide an epoxy resin composition having excellent curing performances, they can provide an epoxy resin cured coating film having excellent film performances and they can provide an epoxy resin cured product having excellent physical properties compared to other polyamine compounds and a curing agent for epoxy resins using said other polyamine compounds as a raw material.H2N—H2C-A-CH2—NH2  (1)wherein A is a phenylene group or a cyclohexylene group
On the other hand, however, an epoxy resin composition using a diamine represented by the formula (I) or a curing agent for epoxy resins using said diamine as a raw material easily produces carbamate or carbonate by absorbing carbon dioxide or water vapor in the atmosphere. Generation of carbamate or carbonate is unfavorable because there is a tendency that deterioration of performances of an epoxy resin cured coating film such as gloss, clarity or leveling, deterioration of drying performance, i.e. becoming difficult to dry, deterioration of physical properties of an epoxy resin cured product such as intensity, deterioration of adhesiveness to a substrate whereon the cured coating film is formed will occur. In addition, appearance of a coating film will become inferior because whitening may easily occur by deterioration of water resistance.
Various additives are used for the purpose of improving surface properties such as a surface appearance, drying performance and water resistance of an epoxy resin cured coating film and an epoxy resin cured product. However, the following problems may often occur though using additives: improvement of water resistance of an epoxy resin cured coating film is not satisfactory though the drying performance is improved, improvement of drying performance of an epoxy resin cured coating film and an epoxy resin cured product is not satisfactory though water resistance is improved, and clarity of an epoxy resin cured coating film is deteriorated though drying performance and water resistance are improved. In addition, deterioration of adhesiveness to a substrate may occur by using additives.
It is well known to use an addition reaction product of a diamine represented by the formula (I) and epoxy resins, i.e. an epoxy adduct, as a curing agent for epoxy resins (see Japanese Patent Publication No. 03-239719, Japanese Patent Publication No. 11-269252). However, satisfactory properties of cured products in terms of the appearance of coating films such as gloss, clarity and leveling, water resistance and the like can not be achieved only by using such an epoxy adduct.